The invention is based on patent application Nos. 2000-20047 Pat., 2000-20807 Pat., 2000-21274 Pat., 2000-21482 Pat., 2000-22933 Pat. and 2000-372845 Pat. filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an image display medium and an image display method, and particularly relates to a reversible image display medium, in which image displaying and image erasing operations can be repeated, and an image display method utilizing the medium.
2. Description of the Background Art
At present, image display is performed, e.g., in the following manners. A person uses a pencil, a pen, paints or the like, and manually writes or draws characters, pictures or the like on an image display medium such as paper sheet. Also, a computer, a word processor or the like is used to display text, graphics or the like on a display such as a CRT display, or output them on a medium such as a paper sheet via a printer for display.
A copying machine or the like may be used for producing duplication, on a medium of paper or the like, of the texts, pictures, graphics or the like, which are produced on the medium of paper or the like by a person or by a printer. A facsimile machine may be used for sending such contents (texts, pictures graphics and others) prepared in the above manner for producing duplication on another medium of paper or the like.
The above image display, which is performed to display the texts, pictures or the like on the image display medium of paper or the like by a pencil, pen or the like, or by an image forming apparatus such as a printer, a copying machine or a facsimile machine operating in a electrophotographic method, an ink-jet method, a heat transfer method or the like, can achieve clear image display in a high resolution, and thus can achieve easy-on-the-eyes display.
However, it is impossible to repeat display and erasure of the images on the image display medium of paper or the like. In the case where the paper is used for writing characters or the like by a pencil, the characters can be erased by an eraser to a certain extent. However, it is difficult to erase completely the characters or the like written in an ordinary density, although it may be possible when written in a light density. The medium of paper or the like cannot be reused except for the case of using the rear surface of the medium, which is not yet used for the image display.
Accordingly, the medium of paper or the like bearing images will be abandoned or burnt when it is not longer required. This results in consumption of a large mount of resources. The printer, copying machine or the like also consume consumable products or materials such toner or ink. For obtaining the new display medium of paper or the like as well as toner, ink or the like, energies and resources are required for producing them. This is contrary to the current demand for reduction in environmental loads.
In contrast to the above, the image display by a display such as a CRT display can repeat the image display and the image erasure. However, the resolution, clarity and precision of images are restricted, as compared with the images displayed by the printer or the like on the paper medium or the like. Due to the relatively low resolution and the light emission from the display, operations for a long time are likely to be hard to eyes.
Electrophoretic display has been proposed as an image display method allowing repetition of the image display and image erasure. In the electrophoretic display method, two substrates including at least one transparent substrate are opposed together with a spacer therebetween to form a closed space therebetween, and the space is filled with a display liquid formed of a dispersion medium and electrophoretic particles, which are dispersed in the dispersion medium and are different in color from the medium. The image display is performed by an application of an electrostatic field and in a color of the particles or a color of the dispersion medium.
The display liquid is usually formed of isoparaffin-contained dispersion medium, particles of titanium dioxide or the like, dyes applying contrast in color to the particles, and an additive such as a surface active agent, or a charge applying agent.
In the electrophoretic display, the display is performed by utilizing contrast between particles of a high refractive index (e.g., titanium dioxide particles) and colored insulating liquid, and therefore the particles cannot hide the colored liquid to a high extent, resulting in a low contrast. Further, settling and condensation of particles are liable to occur due to a very large difference in specific gravity between the particles and the dispersion medium in the display liquid. This is liable to lower the display contrast. Further, it is difficult to display the images with high stability for a long time, and remaining of last images is liable to occur. Further, the degree of charging of the particles in the liquid significantly changes with time, which also impairs the stability of the image display.
Accordingly, an object of the invention is to provide reversible image display medium and an image display method, which allow repeating of image display and image erasure, and thereby can reduce consumption of image display media of paper or the like relating to the conventional image display and consumable materials such as developer and ink so that a current demand for reduction in environmental loads can be satisfied.
Another object of the invention is to provide a reversible image display medium and an image display method, which allow display of images in good contrast and high quality.
Still another object of the invention is to provide a reversible image display medium and an image display method, which allow display of images in high resolution and high quality.
Yet another object of the invention is to provide a reversible image display medium and an image display method, which allow stable display of high-quality images for a long time.
Further another object of the invention is to provide a reversible image display medium and an image display method, which can suppress remaining of last images, and therefore can exhibit good reversibility so that images of good quality can be displayed.
A further another object of the invention is to provide a reversible image display medium and an image display method, which can reduce a drive voltage required for image display.
A further object of the invention is to provide a reversible image display medium and an image display method, which can suppress irregularities in displayed images.
The invention provides reversible (in other words, reusable) image display mediums and image display methods described below.
(1) First Reversible Image Display Medium and First Image Display Method
(1-1) First Reversible Image Display Medium
A reversible image display medium including:
two sheets opposed to each other with a predetermined gap therebetween;
one or more developer accommodating cells formed between the two sheets, and each having a periphery surrounded by a partition wall; and
dry developer contained in each of the cell(s), wherein
the dry developer contains at least two kinds of frictionally chargeable dry developer particles having different chargeable polarities and different optical reflection densities.
(1-2) First Image Display Method
An image display method including the steps of:
preparing the above first reversible image display medium having at least two kinds of the dry developer particles forming the dry developer within the developer accommodating cell(s), and frictionally charged to have the charged polarities different from each other; and
displaying an image by forming a predetermined electrostatic field for each pixel in accordance with the image to be displayed and thereby moving the developer particles, with the developer particles contained in each of the cell(s) being in the frictionally charged state.
(2) Second Reversible Image Display Medium and Second Image Display Method
(2-1) Second Reversible Image Display Medium
A reversible image display medium including:
two sheets opposed to each other with a predetermined gap therebetween;
one or more developer accommodating cells formed between the two sheets, and each having a periphery surrounded by a partition wall;
dry developer contained in each of the cell(s);
an electrode formed on an inner surface of one of the sheets; and
an electrode formed on an inner surface of the other sheet, and opposed to the electrode, wherein
the dry developer contains at least two kinds of frictionally chargeable dry developer particles having different chargeable polarities and different optical reflection densities.
The electrode on the inner surface of one of the sheets may be formed of a group of independent electrodes formed for the respective pixels.
(2-2) Second Image Display Method
An image display method including the steps of:
preparing the above second reversible image display medium having at least two kinds of the dry developer particles forming the dry developer within the developer accommodating cell(s), and frictionally charged to have the charged polarities different from each other; and
displaying an image by forming a predetermined electrostatic field for each pixel in accordance with the image to be displayed by applying a voltage across the electrodes and thereby moving the developer particles, with the developer particles contained in each of the cell(s) being in the frictionally charged state.
In the reversible image display medium used in this image display method, the electrode on the inner surface of one of the sheets may be formed of a group of independent electrodes formed for the respective pixels.
(3) Third to Fifth Reversible Image Display Mediums and Third Image Display Method
(3-1) Third Reversible Image Display Medium
A reversible image display medium including:
two sheets opposed to each other with a predetermined gap therebetween;
one or more developer accommodating cells formed between the two sheets, and each having a periphery surrounded by a partition wall; and
dry developer contained in each of the cell(s), wherein
the dry developer contains at least two kinds of frictionally chargeable dry developer particles having different chargeable polarities and different optical reflection densities,
each of the sheets has a thickness from 5 xcexcm to 100 xcexcm,
the gap between the sheets is in a range from 20 xcexcm to 300 xcexcm, and
the medium has a whole thickness of 30 xcexcm to 500 xcexcm.
(3-2) Fourth Reversible Image Display Medium
A reversible image display medium including:
two sheets opposed to each other with a predetermined gap therebetween;
one or more developer accommodating cells formed between the two sheets, and each having a periphery surrounded by a partition wall; and
dry developer contained in each of the cell(s), wherein
the dry developer contains at least two kinds of frictionally chargeable dry developer particles having different chargeable polarities and different optical reflection densities, and
at least one of the two sheets has a surface resistance of 1010 ohm/square-1016 ohm/square (1010 ohm/xe2x96xa1-1016 ohm/xe2x96xa1) on its outer surface.
(3-3) Fifth Reversible Image Display Medium
A reversible image display medium including:
two sheets opposed to each other with a predetermined gap therebetween;
one or more developer accommodating cells formed between the two sheets, and each having a periphery surrounded by a partition wall; and
dry developer contained in each of the cell(s), wherein
the dry developer contains at least two kinds of frictionally chargeable dry developer particles having different chargeable polarities and different optical reflection densities, and
at least one of the two sheets has a surface resistance of 107 ohm/square (107 ohm/xe2x96xa1) or less on its outer surface.
(3-4) Third Image Display Method
An image display method including the steps of:
preparing one of the above third to fifth reversible image display mediums having at least two kinds of the dry developer particles forming the dry developer within the developer accommodating cell(s), and frictionally charged to have the charged polarities different from each other; and
displaying an image by forming a predetermined electrostatic field for each pixel in accordance with the image to be displayed and thereby moving the developer particles, with the developer particles contained in each of the cell(s) being in the frictionally charged state.
(4) Sixth Reversible Image Display Medium
A reversible image display medium including:
two sheets opposed to each other with a predetermined gap therebetween;
one or more developer accommodating cells formed between the two sheets, and each having a periphery surrounded by a partition wall; and
dry developer contained in each of the cell(s), wherein
the dry developer contains at least two kinds of frictionally chargeable dry developer particles having different chargeable polarities and different optical reflection densities, and at least one kind of the developer particles are electrically nonconductive particles.
(5) Seventh Reversible Image Display Medium
A reversible image display medium including:
two sheets opposed to each other with a predetermined gap therebetween;
one or more developer accommodating cells formed between the two sheets, and each having a periphery surrounded by a partition wall; and
dry developer contained in each of the cell(s), wherein
the dry developer contains at least two kinds of frictionally chargeable dry developer particles having different chargeable polarities and different optical reflection densities, and at least one kind of the developer particles are magnetic particles.
(6) Eighth Reversible Image Display Medium
A reversible image display medium including:
two sheets opposed to each other with a predetermined gap therebetween;
one or more developer accommodating cells formed between the two sheets, and each having a periphery surrounded by a partition wall; and
dry developer contained in each of the cell(s), wherein
the dry developer contains at least two kinds of frictionally chargeable dry developer particles having different chargeable polarities and different optical reflection densities, and
a rate Sn/So of an area Sn of a non-image portion with respect to a medium unit area So is in a range from 0.0001 to 0.5.
(7) Ninth Reversible Image Display Medium
A reversible image display medium including:
two sheets opposed to each other with a predetermined gap therebetween;
one or more developer accommodating cells formed between the two sheets, and each having a periphery surrounded by a partition wall; and
dry developer contained in each of the cell(s), wherein
the dry developer contains at least two kinds of frictionally chargeable dry developer particles having different chargeable polarities and different optical reflection densities, and
a value of (1xe2x88x92Sa/Sb) in a range from 0.0001 to 0.5 is obtained from arbitrary one of the developer accommodating cell(s) or arbitrary two or more successively arranged developer accommodating cells, assuming that Sa represents an area of an image display region provided by the above one developer accommodating cell or the cell group including the plurality of successively arranged developer accommodating cells, and Sb represents an area surrounded by a center line of the partition wall defining an outer periphery of the one developer accommodating cell or an area surrounded by a center line of the partition wall defining an outer periphery of the above cell group including the plurality of developer accommodating cells.
In this ninth reversible image display medium, a rate of the image display region is defined from a viewpoint different from that of the eighth reversible image display medium.
(8) Tenth Reversible Image Display Medium
A reversible image display medium including:
two sheets opposed to each other with a predetermined gap therebetween;
one or more developer accommodating cells formed between the two sheets, and each having a periphery surrounded by a partition wall;
dry developer contained in each of the cell(s); and
a developer movement suppressing member arranged between the two sheets for suppressing movement of the dry developer within the developer accommodating cell(s), wherein
the dry developer contains at least two kinds of frictionally chargeable dry developer particles having different chargeable polarities and different optical reflection densities.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.